1. Field of the Invention
The present invention relates in general to ground water sampling and, more particularly, to a baffle apparatus for use in wells.
2. Description of the Related Art
During the winter, the shallow water in wells cools. When the shallow water becomes cooler than the deeper water in the well, the well water “turns over” and begins a process of in-well convection that continues through the winter. The convection transports dissolved oxygen (DO) from the surface of the water column to deeper parts of the well. When the aquifer is anaerobic, the transport of DO to the screened interval can adversely affect the ability of passive samplers to produce accurate concentrations of oxygen-sensitive solutes, such as iron and other redox indicators and microbiological data. During low-flow sampling, the pumped water may be a mixture of convecting water from within the well casing and aquifer water moving inward through the screen. This mixing of water during low-flow sampling can substantially increase equilibration times of indicator parameters, cause false stabilization of indicator parameters, give false indications of the redox state, and provide microbiological data that are not representative of the aquifer conditions. In-well convection is described in more detail in “Influence of In-Well Convection on Well Sampling” by D. A. Vroblesky et al., U.S. Geological Survey Scientific Investigations Report 2006-5247, pp. 1-13, 2006, and in “Influence of Dissolved Oxygen Convection on Well Sampling” by Vroblesky, D. A., Casey, C. C., and Lowery, M. A., Ground Water Monitoring and Remediation, v. 27, no. 3, Summer 2007, pp. 49-58, both of which are incorporated herein by reference. Because this problem is likely to be widespread in a variety of climate regimes, there is a need for an inexpensive, simple device to mitigate in-well convection.